Fix: Use plural resource names in createNote URL construction

- Changed  to s to use the correct plural form in API endpoints

- This fixes 404 errors when trying to add notes to issues or merge requests

- Added a test file to verify the fix

- Conforms to GitLab API documentation which uses plural resource names (issues, merge_requests)

index.ts

@@ -585,7 +585,7 @@ async function createNote(
   const url = new URL(
     `${GITLAB_API_URL}/api/v4/projects/${encodeURIComponent(
       projectId
-    )}/${noteableType}/${noteableIid}/notes`
+    )}/${noteableType}s/${noteableIid}/notes` // Using plural form (issues/merge_requests) as per GitLab API documentation
   );
 
   const response = await fetch(url.toString(), {